Casting level-control device for a continuous casting installation



. y 2, 1969 JEAN-PIERRE WEISS 3,456,714

CASTING LEVEL-CONTROL DEVICE FOR A CONTINUOUS CASTING INSTALLATION Filed March 3, 1967 2 Sheets-Sheet 1 Fig. I

' INVENTO TERM-PIER E 3 BY:% Q

Filed March 5, 1967 y 1969 JEAN-Pl RRE wel'ss 3,456,714

CASTING LEVELCONTRO DEVICE FOR A CONTINUOUS CASTING INSTALLATION 2 Sheets-Sheet 2 INVENTOR Jew fie Rae Hass- BYQQJAM 5 MW (111 ODMJMJ/A 3,456,714 CASTING LEVEL-CONTROL DEVICE FOR A CONTINUOUS CASTING INSTALLATION Jean-Pierre Weiss, Zurich, Switzerland, assignor to Erik Olsson AG., Zurich, Switzerland, a corporation of Switzerland Filed Mar. 3, 1967, Ser. No. 620,475 Claims priority, application Germany, Mar. 5, 1966, 11,501 Int. Cl. B22d 11/10, 45/00; G011? 23/22 US. Cl. 164-154 12 Claims ABSTRACT OF THE DISCLOSURE A control device for regulating the casting level of a continuous casting installation wherein a measuring location is arranged in the neighborhood of the inner wall of the mold and a thermal sensitive element is disposed at such measuring location for sensing the thermal conditions thereat in order to determine the height of the casting level of the metal Within the mold. Furthermore, in order to reduce the time constant or response time of the thermal sensitive element the surfaces which directly surround the measuring location are disposed in a closed cycle for a cooling agent.

BACKGROUND OF THE INVENTION The present invention pertains to an improved control device for regulating the casting level of the metal within the mold of a continuous casting installation.

With most of the known processes for the continuous casting of metal, particularly steel, the liquid metal comes out of a suitable vessel, for instance a bottom-pour ladle, a tilting or lip-poured ladle, a holding furnace and so forth and initially arrives at a refractory intermediate vessel. An outlet or pouring nozzle is mounted at the floor of this intermediate vessel. This pouring nozzle serves to conduct the liquid metal into an open throughfiow ingot mold, which is generally water cooled, and within which this metal solidifies in the outer marginal zones owing to the cooling action. The metal strand which is at least partially solidified is continuously withdrawn at the lower end of the ingot mold. For this purpose there are provided so-called propelling or withdrawal rollers which engage the strand. The rotational speed of these withdrawal rollers is infinitely variable. During the manual control of the casting speed the casting level of the metal in the mold is observed, and which advantageously is maintained at a constant relative height. In order to achieve such, the withdrawal speed of the strand is accommodated to the quantity of steel delivered to the mold from the casting or pouring vessel. On the other hand, with a constant withdrawal speed of the strand, it is also possible to control the quantity of steel which flows into the mold. Still in this instance the casting level serves as a reference value for the operating personnel. Now, for quite some time attempts have been made to determine this reference value in a technological manner and to employ the obtained information for the automatic control of the apparatus, whether it be for the regulation of the infeed quantity or the withdrawal speed. A number of different techniques have already been extensively developed, of which the three most important will be hereinafter explained and their primary drawbacks will also be touched upon.

The determination of the casting level by means of radioactive rays requires an apparatus which, owing to its relative danger, can only be used by highly trained personnel. Apart from this, it is necessary to construct nited States Paten 0 the mold in such a manner that the major portion of the absorption of rays takes place in the liquid metal and not in the mold itself, in order to be able to obtain a sufliciently exact signal. This requires the utilization of thin-walled molds, which also brings about a limitation in the application of the process.

According to another prior art technique information concerning the relative height of the casting level in the mold can also be obtained by measuring the radiation intensity in the infrared region by means of a photocell or a photo-resistor. Theoretically, the measured potential or voltage must be proportional to the reflecting surface of the casting level. Appropriate experiments have, however, shown that a number of disturbing factors, such as flame, smoke, reflection of the walls of the mold, unsteady casting jet and so forth, have an extensive influence upon the measurement result. Apart from this, this technique is impractical insofar as no foreign bodies can appear at the line of sight between the casting level and the photocell, but which when considering the nature of the continuous casting process cannot be prevented.

Moreover, it has also already been proposed to mount at the ingot mold commercially available thermocouple elements which are used for localizing the casting level. The internal temperature at the chosen locations of the water cooled copper mold does, in fact, vary in dependency upon the momentary position of the casting level. However, thermocouple elements are not particularly suitable for measuring the occurring temperature fluctuations because these elements operate relatively slowly which, in the first instance, is based upon the fact that there is a poor heat transfer between the copper of the mold and the thermocouple element and, furthermore, the relatively large heat content of the neighboring portions of the mold falsifies the measurement result.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an improved control device of the type described which overcomes the previously mentioned drawbacks of the prior art structures.

Still, a further more specific object of the present invention relates to an improved control device for controlling the casting level of a continuous casting installation and which is extremely reliable in operation, absolutely safe and also quite simple to use, and provides for continuous monitoring of the casting level of the metal in the mold.

Another significant object of this invention relates to an improved control device for controlling the casting level of the metal Within the mold of a continuous casting installation, which control device is extremely sensitive in operation, provides for extremely rapid determination of the height of the casting level and for controlling such that a substantially constant casting level is maintained throughout the casting operation.

Now, in order to implement these and still further objects of the invention which will become more readily apparent as the description proceeds, the inventive control device for continuous casting installations or plants comprises a measuring location for determining the height of the casting level of the metal Within a mold. This measuring location is arranged in the neighborhood of the inner wall of such mold and is sensed by a thermal sensitive element. According to one important aspect of the invention it is contemplated to reduce the time constant or response time of the thermal sensitive element by arranging the surfaces directly surrounding the measuring location in a closed cycle or circulation system for a cooling agent.

Owing to this physical structure of the inventive control device there is advantageously obtained an extensive screening of the measuring location and the measuring element with regard to the neighboring portions of the mold, and therefore, there is practically only determined temperature variations or changes which occur directly in the wall portion located radially within the measuring location. These temperature changes are primarily attributable to the direct approach of the casting level at the measuring location when the casting level increases or the withdrawal or distancing of such casting level from such measuring location when the casting level drops. Such type measuring device requires considerably less expenditure than the previously explained prior art apparatuses, and obviously provides a considerable advantage thereover.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood, and objects other than those set forth above, will become apparent, when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIGURE 1 schematically illustrates a preferred embodiment of inventive control device; and

FIGURE 2 is a fragmentary, enlarged cross-sectional view depicting a detail of the mold.

DESCRIPTION OF THE PREFERRED EMBODIMENT Describing now the drawings, it will be seen that in the continuous casting installation or plant depicted in FIG- URE l the liquid metal flows out of the pouring or casting vessel 2, which possesses a nozzle 6 which can be closed by a suitable stopper 4, in the form of a freefalling stream or jet 8 and enters a water-cooled ingot mold 10. The strand 12 which is completely or partially solidified in the mold 10 is withdrawn through the agency of appropriate propelling or withdrawal rollers 14. The quantity of the liquid metal introduced into the mold 10 and the feed velocity of the strand 12 are accommodated to one another in such a manner that the casting level of the metal in the mold 10 is maintained at an approximately constant elevation or level. By controlling the rotational speed of the withdrawal rollers 14 or by regulating the discharge quantity of metal from the nozzle 6 with the aid of the stopper 4 such requirement is fulfilled and there is achieved an equilibrium condition.

Now, in order to obtain this objective with the illustrated embodiment of continuous casting installation the rotational speed of the withdrawal rollers 14 is influenced by a control device. This control device embodies a temperature sensing element, here in the form of a thermal sensitive resistor 16 (FIGURE 2) which is mounted in the mold 10, and the resistance value of which is influenced by the temperature acting upon such thermal sensitive resistor 16. This temperature which acts upon the thermal sensitive resistor 16 is extensively dependent upon the position of the casting level with regard to the resistor 16 and it will become that much greater the closer the casting level approaches from below the level or elevation at which the resistor 16 is located.

Now, as will be readily recognized by referring to the fragmentary, cross-sectional view of the ingot mold 10 of FIGURE 2 the thermal sensitive resistor 16 is located in the neighborhood of the inner surface or wall 18 of the mold 10, and specifically, at the base or floor surface 19 of a bore or recess 20 which extends substantially radially with respect to the axis of the mold 10. The resistor 16 is embedded in an insulator 22 formed of Teflon, and specifically in such a manner that this resistor 16 is pressed with one of its side surfaces against the metal of the mold 10, yet is sealed from the inner compartment of the bore 20. The insulator 22, in turn, is pressed against the floor or bottom 19 of the bore 20* by means of a holder 24 having a contact or press-on screw means 26 and is simultaneously centrally retained in such bore 20, so that there is formed an annular chamber or compartment providing a cooling chamber 28.

The base of the cooling chamber 28, which is formed by a substantially ring-shaped cooling surface 21 is closer to the inner surface or wall 18 of the mold than the bottom surface 19 of the bore 20, whereby the crosssection is narrowed for the fiow of heat out of the neighboring portions of the mold 10. Moreover, the holder 24 bears against a snap ring 30 which is mounted in the bore 20 having the side walls 20a. A bore 32 which extends at" an inclination to the axis of the mold 10 merges with the annular cooling compartment 28. This inclined bore 32 is connected in a manner which is not further illustrated in FIGURE 2 to a closed cycle or circulation system for a suitable cooling medium, such as water for instance. Bore 20 is likewise connected to this closed cycle or circulation system and serves for the return of the cooling agent arriving from the bore 32. The measuring cable 34 connected with the resistor 16 can be conducted out of the mold 10 by means of the inclined bore 32.

As will further be recognized by referring to the drawings, the portions of the mold 10 which neighbor the resistor 16 are subjected to the influence of the cooling agent with the exception of the wall portion 18a which separates such resistor 16 from the inner compartment of the mold 10. Since the resistor 16 is in intimate heatconducting communication and effectively screened off with regard to the remaining portions of the mold by the insulator 22 and the cooling agent, there is primarily transmitted to such resistor 16 the temperature changes at the partition wall 18a and which are determined by the variations in the position of the casting level.

The signal changed by the thermal sensitive resistor 16 is received by a suitable signal device 36 and transmitted through the agency of a control device 38 to a pre-control unit 40 which, in turn, operates a suitable servomotor 42. This servomotor 42 acts upon an adjusting rod or linkage 44 of a hydrostatic drive 46 which changes the rotational speed of the withdrawal rollers 14. The rod or linkage means 44 can also be manually actuated by the hand-control lever 48. Depending upon the change of the signal by the resistor 16 the rotational speed of the withdrawal rollers 14 also change in the manner that, if the casting level climbs above a predetermined level or position the withdrawal speed of the metal strand increases, whereas if the casting level drops this speed of withdrawal is reduced. With a falling casting level the cooling of the surroundings of the temperature measuring location, generally designated by reference character M, is particularly important in order to guarantee a quick response of the control device. The increase of the casting level has a very rapid effect owing to the temperature difference between, for instance, liquid steel (e.g. D C.) and the wall of the mold 10 (e.g. 280 C.).

Continuing, as indicating means for the maximum and minimum permissible height of the casting level thermal sensitive elements, such as the elements 50 and 60, which may be similar to the thermal sensitive resistor 16, are located at suitable spacing above and beneath the measuring location M and mounted in the mold 10, as shown in FIGURE 2, and these additional thermal sensitive elements 50, 60' determine the reference levels. The lower thermal sensitive element 60 can additionally serve for controlling the start of the machine when beginning casting.

With most of the known continuous casting processes the mold 10 is subjected during casting to an oscillatory movement in a direction extending parallel to its longitudinal axis. Thus, in FIGURE 1 there is schematically illustrated a drive mechanism D which is capable of imparting such an oscillatory movement to the mold 10. When this happens, the mold 10 and, therefore, naturally also the measuring location M moves relative to the casting level independently of the fact whether the absolute height of the casting level in the meantime changes or does not change. However, in order to be still able to carry out a useable measurement of the height of the casting level it can 'be useful, under certain circumstances, to also simultaneously continuously determine the position of the displaced mold. To this end, there may be employed for instance an induction coil 51 (FIG- URE 1) having a core 52 which moves together with the mold 10, whereby the changes of the induction current are delivered for instance to the signal device 36. Finally, as also shown in FIGURE 1 a circulation system or closed cycle for a cooling medium, such as Water, and generally designated by reference character C, can be provided so that the cooling agent is not only circulated through the mold but also through the bore 32 for the measuring location M. Furthermore, instead of employing an induction coil 51 and core 52 it is conceivable to use a capacitor which, for instance, might have one plate connected for movement with the displaceable mold 10, or further, to employ a potentiometer having a movable tap connected with the displaceable mold 10.

The use of the electric resistance element, such as the thermal sensitive element 16, in conjunction with the described construction of the measuring location M has the advantage that it delivers very quickly an exact measuring signal.

While there is shown and described a present preferred embodiment of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,

What is claimed is:

1. In a continuous casting installation including a mold having an inner and outer wall, the improvement of a control device for controlling the casting level of the metal within said mold, said control device comprising:

means defining a temperature measuring location neighboring and in thermal communication with said inner wall of said mold;

a thermal sensitive element disposed at said temperature measuring location for sensing thermal conditions thereat in order to determine the height of the casting level;

cooling means for cooling the mold surfaces directly surrounding said temperature measuring location and for effecting a thermal isolation of said temperature measuring location to thus reduce the response time of said thermal sensitive element.

2. In a continuous casting installation as defined in claim 1, wherein said cooling means defines a closed cycle through which a cooling agent is circulated.

3. In a continuous casting installation as defined in claim 1, said outer wall of said mold being provided with a bore having a bottom surface, said bottom surface of said bore providing at least a portion of said temperature measuring location, said bore having side surfaces, said side surfaces being connected with said bottom surface by a substantially ring-shaped cooling surface which completely surrounds said bottom surface, a substantially annular cooling compartment disposed within said bore and bounded by said ring-shaped cooling surface, said cooling compartment operably communicating with said cooling means.

4. In a continuous casting installation as defined in claim 3, wherein said substantially ring-shaped cooling surface is formed by a recess directed towards said inner wall of said mold.

5. In a continuous casting installation as defined in claim 1, wherein said thermal sensitive element comprises an electrical resistance element.

6. In a continuous casting installation as defined in claim 1, wherein said cooling means defines a closed cycle through which a cooling agent is circulated, said cooling means simultaneously serving for cooling of the mold.

7. In a continuous casting installation as defined in claim 6, wherein said cooling agent is water.

8. In a continuous casting installation as defined in claim 1, further including thermal sensitive means mounted at said mold at a location above said thermal sensitive element in order to indicate a maximum height of cast metal within said mold.

9. In a continuous casting installation as defined in claim 1, further including thermal sensitive means mounted at said mold at a location below said thermal sensitive element in order to indicate a minimum height of cast metal within said mold.

10. In a continuous casting installation as defined in claim 9, wherein said lower located thermal sensitive means mounted at said mold serves to control the starting of the continuous casting installation.

11. In a continuous casting installation as defined in claim 1, further including means for oscillating said mold, and means for continuously determining the position of said oscillating mold.

12. In a continuous casting installation as defined in claim 11, wherein said means for continuously determining the position of said oscillating mold includes inductance means.

References Cited UNITED STATES PATENTS 2,246,563 6/ 1941 Winters 73-295 X 2,743,492 5/1956 Easton 164-281 X 2,768,413 10/ 1956 Alexanderson 164-155 2,772,455 12/ 1956 Easton et al. 164155 X 3,247,714 4/1966 Schwabe et al. 3,300,820 1/1967 Tiskus et a1 164-455 FOREIGN PATENTS 697,669 9/1953 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner R. SPENCER ANNEAR, Assistant Examiner US. Cl. X.R. 73--295 

